A gas spring is a type of spring that, unlike a typical metal spring, uses a compressed gas, contained in a cylinder and variably compressed by a piston, to exert a force. Gas springs are used frequently in automobile construction, where they are commonly used to support the weight of vehicle doors while they are open. They are also used in furniture, medical, and aerospace applications. In particular, gas springs have been adapted for use in adjustable lift columns for furniture and medical applications.